The problem with this mod is that it is easy to get to 300% productivity depending on what level you are on regarding of research (if the research only requires red research). Can it be balanced to include milestone requirements for all research types (i.e. if you get to level 3 of iron plates, it now requires green science, then gray science (at level 4), then blue science (at level 5), then purple (level 6), then yellow at level 7 (calling it by color of science), then after that, it requires space science at level 8 and other science packs onwards at more expensive rates - if sciences start with more different types of science packs at the start, same thing. It balances things out so you don't easily get the max research early, but requires you to play the game to max things out.

Right now the mod just takes the science packs from the research unlocking the item recipe, because there is no defined pack progression and just adding packs might make things un-researchable (I think there is at least one mod that adds basic science packs which are not present in normal labs). So, it's not completely clear how to do what you want.

I will think about it.

Technically once you research the next pack, you can continue with the research of that research until the next milestone.

What is the "next research pack"? I really don't want to hardcode progression.

Was looking for a mod that added more Promethium based science but even the generated promethium pack productivity this adds doesn't use it, sadly.

Outside of recursively spidering the tech tree I doubt you'll find an elegant solution to the balance issue.

Because this is dealing with productivity, I think it would be fair to say at a minimum automation, production, and utility science are a must-have for every single tech prototype this generates. This would even out over using the mod at the early game. Gears, for example, are trivial with this mod.
Adding to that any prod. tech from Space Age should include space science at a minimum is another idea.
I would, honestly, require promethium packs for every single space age based tech this mod generates.

You could really open the mod to customization and experimentation by adding a few new startup config options.
% productivity added per research is one, you set it to 10%, what if it could scale? level 1-10 is 1%, 11-20 is 5%, then 10% thereafter.
I had my last modded game able to push 587,000 science per minute a new record for me at least.

I added a setting to include additional science packs to all researched added by this mod which should help a bit. It is set to red+green+blue+purple science by default, but you can make it require prometheum science instead, for example.